The advertising has to be done. The intended outcome is that the public believes it participated in a meaningful, unrigged, honest, election. If the process of electing the government looks rigged, if it doesn't include the appearance of persuading the public, the public will not attach legitimacy to the elected government. So the elites spend a bunch of money to propagate advertisements, in order to create a perception that public persuasion is necessary in advance, as if the choice at the ballot box makes a difference to the ruling class. Rigging the ballot box or buying delegates is sometimes but not always necessary to prevent a candidate that is unacceptable to the ruling class from getting into elected office.
Again, you are very perceptive. Keep projecting the appearance of a fair election. Bush was supposed to have won this with a $140,000,000 in media ad buys.
Polling plays into this as well.
Have you noticed the lack of the polling by the Majors in certain caucus states and states with voterless voting. The same goes for the lack of exit polling after they have thrown a state election.